Apparatus for detecting relation of speeds of two different elements



Nov. 23, 1943.

APPARATUS FOR DETECTING RELATION OF SPEEDS OF TWO DIFFERENT E J. CANETTA ETAL LEMENTS Original Filed Aug. 51, 1940 2 Sheets-Sheet 1 ATTORN EY Nov. 23, 1943. c E ETAL 2,334,863 APPARATUS FOR DETECTING RELATION 0F SPEEDS OF TWO DIFFERENT ELEMENTS Original Filed Aug. 31, 1940 2 Sheets-Sheet 2 I Patented Nov. 23, 1943 UNITED STATES PATENT OFFICE APPARATUS FOR DETECTING RELATION OF SPEEDS OF TWO DIFFERENT ELEMENTS John Canetta, Wilkinsburg, and Paul N. Bossart, Cheswick, Pa., assignors to The Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Original application August 31, 1940, Serial No. 354,938. Divided and this application January 30, 1941, Serial No. 376.598

' 5- Claims. (Cl. 175-183),

This invention relates to apparatus for detectins the relation of speeds of two different elements and has particular relation to apparatus for detecting a differential in excess of a certain amount between the rotational speeds of two different rotary elements, the present application being a division of our prior copending application, Serial No. 354,938, filed August 31, 1940, now Patent 2,277,035.

There are numerous mechanical mechanismsa manner to restore them to speeds having less I than the certain differential.

More specifically it is an object of our invention to provide apparatus of the type indicated in the foregoing object and characterized by novel means for detecting a predetermined differential between the frequencies of two separate sources of alternating current having frequencie corresponding respectively to the speeds of the two rotary elements.

In illustrating the utility of our invention we have shown it in connection with a fluid pressure type of brake equipment for railway cars, but it should be understood that this is only one of many possible uses to which our invention may be put.

As is well known, if the brakes are applied on a vehicle wheel to a sufficient degree to exceed the adhesion or rolling friction between the rim -of the wheel and road surface or the rails on which the wheel rolls, the wheel decelerates at an abnormally rapid rate to a locked-wheel condition and slides. The term "slip or "slipping condition as employed herein refers to the rotation of a vehicle wheel at a speed less than a speed corresponding to vehicle speed at a given instant, whereas the term "slide or sliding condition" refers to the dragging of a vehicle wheel along a road surface or rail in a locked condition. The distinction between the two terms should be borne in mind.

Various types of apparatus have been proposed for detecting the slipping condition of a vehicle rangement for detecting the slipping condition of a vehicle wheel by comparison to the speed of a non-slipping wheel and so controlling the brakes as to cause the slipping wheel to be restored to vehicle speed.

The above objects, and other objects of our invention which will be made apparent hereinafter, are attained by means of several embodiments of our invention subsequently to be described and shown in the accompanying drawings,- wherein Fig. 1 is a simplified diagrammatic view, showing a brake control equipment for a single railway car, of the two truck type, having one embodiment of my invention applied thereto,

Fig. 2 is an enlarged plan view, partly in section, showing details of the commutator devices associated with the individual wheels or wheel.

units shown in Fig. 1, and

Fig. 3 is an enlarged diagrammatic view, showing a modified type of relay which may be substituted for the type of relay device shown in Fig. 1.

Description of embodiment shown in Fig. 1

Referring to Fig. 1, the brake control equip ment shown therein is that for a single car having a four-wheel truck H at one end thereof and a four-wheel truck I! at the opposite end thereof. Each truck has two separately rotatable wheel units comprising two wheels I3, only one of which is shown in the drawing, connected by and fixed to a connecting axle H in conventional manner.

The brakes associated with the wheels l3 may be of the usual clasp type in which the brake shoes are operated into and out of engagement with the rim or tread of the wheels through brake rigging (not shown) in response to the supply of fluid under pressure to and the release of fluid under pressure from brake cylinders I5.

The term wheel unit as employed herein may designate a single wheel or any number of wheels mechanically connected, as by an axle, to rotate together. shown for each wheel truck, one brake cylinder being effective to operate the brakes associated with one wheel unit and the other brake cylinder being effective to operate the brakes associated with the other wheel unit of the same truck. Obviously, any desired number of brak cylinders may be employed.

The brake cylinder l5 associated with one of the wheel units of the truck II is of smaller diameter than the others so that the effective force thereof for a given fluid pressure "supplied to the brake cylinders is less than that of the other brake cylinders. The wheel unit with which this smaller brake cylinder is associated will hereinafter be referred to as the "underbraked wheel unit. The purpose of the smaller brake cylinderfor the one wheel unit is to so In Fig. 1 two brake cylinders are.

limit the degree of application of the brakes associated with the wheel unit that at no time can the wheels of this wheel unit slip but rotate at all times in accordance with the speed of travel of the car. The manner in which this feature is utilized will be made apparent hereinafter.

Fluid under pressure may be supplied to the brake cylinders I5 and released therefrom, under the control of the operator of the vehicle, by any suitable apparatus. For simplicity, we have illustrated an apparatus of the straight-air type employing a train pipe, hereinafter referred to as the control pipe H, to which the brake cylinders I5 are connected by branch pipes I8, and a manually operated brake valve I! of the selflapping type for controlling the pressure in the control pipe I! and the connected brake cylinders I5. The pneumatic brake control equipment further includes a source of fluid under pressure, such as a reservoir 2| that is normally charged to a certain pressure such as one hundred pounds per square inch by means of a fluid compressor not shown, and a train pipe, hereinafter referred to as the supply pipe 22, connected to the reservoir 2| and charged to the pressure therein.

The control pipe I! and supply pipe 22 extend, in conventional manner, from one end of a car to the other and are provided at the ends thereof with suitable angle cocks 23 and hose couplings 24 for connecting the sections of the pipes on successive cars in the usual manner.

The brake 'valve I 9 is connected to the pipes l1 and 22 by branch pipes 25 and 26 respectively, in each of which a manually operated valve 21 is interposed. The valves 21 are in open position when it is desired to have the brake valve I! control the pressure in the control pipe l1. When it is desired to control the pressure in the pipe II by means of a brake valve corresponding to the brake valve IS on another car, the valves 21 are closed, thus cutting the brake valve IQ of Fig. 1 out of operation.

The brake valve I8 is of well-known construction and accordingly a functional description thereof is deemed sufllcient for the purposes of the present application. The brake valve I! .has an operating handle i9a which is effective when shifted in a horizontal plane to rotate a rotary operating shaft that in turn causes operation of the valve mechanism of the brake valve. When the brake valve handle Ha is in its normal or brake release position, the valve mechanism of the brake valve is conditioned to cause the release of fluid under pressure from the control pipe I] through an exhaust port and pipe 28 at the brake valve. When the brake valve handle l9a is shifted in a horizontal plane out of its normal position into a so-called application zone, the valve mechanism of the brake valve is operated to cause fluid under pressureto be supplied from the supply pipe 22 and connected reservoir 2| to the control pipe I! to establish a pressure therein which corresponds substantially to the degree of displacement of the brake valve handle out of its normal position.

If the pressure in the control pipe I! tends to reduce for some reason, such as leakage, the valve mechanism of the brake valve is automatically operative to maintain a supply of fluid under pressure to the control pipe so that a pressure corresponding to the position of the brake valve handle is maintained in the control pipe 21. This pressure-maintaining feature of the brake valve II will be referred to hereinafter.

According to our invention, the equipment shown in Fig. 1 further comprises a magnet valve device 31 interposed in the branch pipe ll leading to the brake cylinders of each wheel truck, and a relay device 32 for each of the wheel units of the vehicle except the underbraked wheel unit, adapted to control the magnet valve device 3| of the corresponding wheel truck.

The equipment further includes a source of two-phase alternating-current adapted to have a frequency, hereinafter referred to as the master frequency, proportional to the rotational speed of the underbraked wheel unit of wheel truck II and, associated with each of the other wheel units of the vehicle an individual source of two-phase alternating-current adapted to have a frequency corresponding to the rotational speed of the corresponding wheel unit and hereinafter referred to as the local frequency. The various sources of two-phase alternating-current may be of any desired and suitable construction. As shown, these sources respectively comprise a commutator or rotary switch device 33 driven according to the rotational speed of the corresponding wheel unit, as by direct connection to the end of the corresponding axle l4 in the'manner presently to be described, and a pair of voltage-translating devices or transformers l4 and 35.

The relay devices 32 are so constructed and arranged, as hereinafter to be explained, as to operatively respond to a predetermined difference in the master frequency and the corresponding local frequency which occurs whenever the corresponding wheel unit slips.

Referring in greater detail to the parts of the equipment, the magnet valves 3] for the two wheel trucks are identical and accordingly only that for the wheel truck I I is shown in detail. Each magnet valve 3| comprises a pair of oppositely seating valves 43 and 44 of the poppet type which are normally biased upwardly by a coil spring 45 to unseated and seated positions respectively. With the valves 43 and 44 so positioned, communication is established through the branch pipe l8 from the control pipe I! to the brake cylinders l5. Each magnet valve further comprises an electromagnet winding 46 which is effective, when energized, to actuate a plunger 41 to shift the valves 43 and 44 downwardly to seated and unseated positions respectively. With' the valves so positioned, the communication through the branch pipe I8 from the control pipe to the brake cylinders is closed and an exhaust communication is established through which fluid under pressure is released to atmosphere from the brake cylinders through an exhaust port 48 at a rapid rate. Upon deenergization of the magnet winding 48, the spring 45 restores the valves to the unseated and seated positions thereof, thereby closing the exhaust communication and reestablishing the supply communication to the brake cylinders.

As diagrammatically shown, each relay device 32 comprises a stator element or frame 5| and a rotor 52. Although not shown in detail, it should be understood that the stator element 51 is similar to the stator of an induction motor and includes a laminated magnetic core structure suitably slotted for receiving the stator windings in the conventional manner. The rotor 52 is similar to a conventional squirrel-cage rotor of an induction motor and is suitably mounted on a shaft 53 J'ournaled in the stator frame 5| in manner not shown. The outside diameter of the rotor 52 is such as to provide a suitable air gap between itself and the magnetic core of the stator element I Mounted in conventional manner in the usual slots of the stator core are two sets of polyphase windings, shown as two-phase windings, diagrammatically indicated for simplicity as phases A and B with either of the sumx numbers i and 2 depending upon the particular set of windings. The two-phase windings Al and BI may be associated with the two-phase windings A2 and B2 in any suitable manner as by having the conductorsof corresponding phase windings received in the same slots at different depths. It will be understood that the stator phase-windings may be distributed in the usual manner of induction or synchronous motor stator windings to provide any desired number of magnetic poles such as 2, 4, 3 etc., within the physical limitation of the device.

Attached to one end of the rotor 52 is a contact 51 attached to the stator frame, biases the contact arm in a direction to normally engage a fixed stop 55 on the stator frame 5|. A contact 58 fixed on the contact arm 54 is effective to bridge or connect two stationary contacts 59 and 60, carried in insulated relation on the frame 5| as by an insulating member 6|, when the arm 54 is shifted in a clockwise direction out of its normal position in response to the rotary movement of the rotor 52.

The phase windings Al and Bi of each of the relays 32 are connected to three train wires 31, 38 and 39 over which the two-phase alternatingcurrent or master frequency is supplied in a manner presently to be described. The energization of the windings Al and BI by a two-phase current is effective, in manner well understood by those skilled in the art of induction motors, to produce a magnetic field which rotates in one direction at a speed corresponding to the frequency of the supply.

The phase windings A2 and B2 are so connected and arranged as to be energized by the local frequency or two-phase alternating-current supplied from the corresponding wheel unit source. The arrangement of the phase windings A2 and B2 is such that upon energization, the magnetic field produced thereby rotates in the opposite direction to that of the magnetic field produced by the phase windings Al and BI and at a speed corresponding to the local frequency.

As long as the master frequency supplied to the windings Al and BI and the local frequency supplied to the windings A2 and B2 are the same or substantially so, the respective torques exerted on the rotor 52 in response to each of the oppositely rotating magnetic fields prdouced by the two sets of windings are substantially equal or balanced so that the contact arm 54 remains biased by the spring 56 to the position, as shown, engaging the stop 55 and separating contact 58 from its associated pair of contacts 59 and 60.

When the local frequency supplied to the windings A2 and B2 becomes less than the master frequency supplied to the windings Al and Bi of a particular relay 32, an unbalanced torque is exerted on the rotor varying in degree according to the difference bet-ween the master frequency and rotor 52 of relatively high resistance metal, for

reasons well-known to those skilled in the art of induction motors, in order that an adequately high torque be exerted on the rotor 52 in response to a small difference between the master and local local frequency. When a sufficient difference befrequencies so as to cause engagement of the contact 58 on the contact arm with its associated pair of contacts 59 and 60.

It will be understood that since the underbraked wheel unit of the wheel truck ll rotates at all times at a speed in accordance with the speed of travel of the car, the master frequency corresponds at all times to the speed of travel of the vehicle. The reduction in the local frequency of the two-phase alternating-current supplied to the phase windings A2 and B2 of each relay 32 accordingly reflects the reduction in speed of the individual wheel unit relative to that of the underbraked wheel unit when the individual wheel unit slips. It will accordingly be seen that when ever any of the wheel units other than the underbraked wheel unit begins to slip, the contact 58 on the contact arm 54 of the corresponding relay 32 is automatically and promptly actuated into engagement with its associated pair of stationary contacts 59 and 60.

The switch formed by-the contacts 58, 59 and 60 of each relay 32 serves to control a circuit for energizing and deenergizing the magnet winding 44 of the magnet valve 3| for the corresponding wheel truck. To this end, the contact 60 of each relay 32 is connected to a wire 62 to which one terminal, such as the positive terminal, of a source of direct-current indicated as a storage battery 63 is connected. The contact 59 of the relay 32 associated with the one wheel unit of the wheel truck II is connected by a wire 65 to one terminal of the magnet winding 46 of the magnet valve 3| for the wheel truck II, the opposite terminal of the magnet winding 46 being connected to the opposite terminal of the battery 63 as through a ground connection in the manner shown. The contact 59 of the two relays 32 for the wheel truck I 2 are connected to a wire 66 which is connected to one terminal of the magnet winding 46 of the magnet valve 3| for the wheel truck I2, the opposite terminal of the magnet winding of this magnet valve being connected to the opposite terminal of the battery 63 as through a ground connection in the manner shown.

The manner in which a commutator device 33 cooperate to supply a two-phase alternating-current having a frequency corresponding to the rotational speed of the corresponding wheel unit will now be briefly described.

As seen in Fig. 2, each commutator device 33 comprises a cylindrical element ll of suitable insulating material, such as hard rubber or Bakelite having a flange at one end which is secured to one end of a wheel, axle I4 as by a plurality of screws 13 in such a manner that the element H is coaxial to the axle I4 and rotates in correspondence therewith. Embedded in the element H during the moulding operation, or otherwise suitably aiiixed thereto, is a contact ring 14 having a continuous portion 15 extending circumferentially around the periphery of the element H and an interrupted portion comprising a plurality of spaced contact fingers 19. The contact ring. 14 is preferably integrally formed of suitable material such as copper, brass or alloys thereof.

As will be seen in Fig. 1, there are eight contact fingers 19 of uniform width and spacing separated by portions of the insulating element ll intervening therebetween and resembling somewhat the commutator of a conventional directcurrent electric motor. It will be understood that any desired number of contact fingers 18 may be provided, eight being shown merely for purposes of illustration.

Arranged in a suitable brush holder, not shown, are three brushes I9, 99 and 91 the brush holder being in turn suitably supported within the Journal casing (not shown) at the end of each wheel axle. Brush I9 is so arranged and mounted as to constantly engage only the continuous portion 15 of the contact ring H, whereas the brushes 99 and 9| are arranged in displaced relation thereto so as to engage only the contact fingers 16 of the contact ring H.

The brushes 80 and iii may occupy any angular position relative to each other as long as they are displaced the equivalent of ninety electrical degrees apart. As will be explained more fully presently, each contactfinger I9 is of a width corresponding to one hundred and eighty electrical degrees and each intervening portion of the insulating element ll between successive contact fingers I is likewise of a width corresponding to one hundred and eighty electrical degrees.

The brush 19 of each commutator device 39 is connected by a branch wire 95 to a bus or train wire 99 which is constantly connected by a branch wire 91 to one terminal, for example the positive terminal, of a suitable source of directcurrent voltage, such as storage battery 89.

The brush 80 is connected by a wire 99 to one terminal of the primary winding 34;) of the associated transformer 94, the other terminal of the primary winding of the transformer being connected to a bus wire 9| that is constantly connected to the negative terminal of the battery 98 In a similar manner, the brush BI is connected by a wire 92 to one terminal of the primary winding 95p of the associated transformer 95, the

other terminal of the primary winding of the transformer being connected to the bus wire 9|.

A suitable condenser 99 is connected between the brush l9 and the brush 99, and a similar condenser 99 is connected between the brush I9 and the brush 9|, for'the purpose of reducing ,arcing at the brushes 99 and 9i when the brushes disengage the contact fingers 19.

It will thus be seen that as a commutator device 39 rotates, the primary windings 34p and 95p of the corresponding pair of transformers are successively energized and deenergized at a frequency depending upon the speed of rotation of the commutator device, which is in turn proportional to the speed of rotation of the associated wheel unit. It will also be seen that due to the are likewise displaced ninety electrical degrees in the manner characteristic of two-phase alter.- hating-current.

In the case of the underbraked wheel unit of the wheel truck II, the secondary windings 94s and 95s are so connected to the train wires 31, 38 and 39 as to provide the two-phase alternatingcurrent or master frequency supply to the phase windings Al and BI of all the relays 32.

A speedometer 95, in the form of a frequency meter, is connected across the wires 91 and 99 to record the frequency in one of the phases.

For convenience, the scale of the speedometer is calibrated in miles per hour. Since the underbraked wheel unit of truck I I always rotates at a speed corresponding to vehicle speed, it will be apparent that the speedometer 95 indicates the speed of the vehicle. Speedometer 95 may be located in a convenient location adjacent the brake valve i9 in the control cab of the vehicle so as to be visible by the operator at all times.

In the case of each of the wheel units other than the underbraked wheel unit, the secondary windings 34s and 95s of the corresponding pair of transformers are so arranged and connected as to supply a two-phase altemating-current, having a frequency corresponding to the speed of rotation of the wheel unit and referred to hereinbefore as the local frequency, to the phase windings A2 and B2 of the corresponding relays 32.

The ratio of the number of turns in the primary and secondary windings of th transformers 94 and 35 in uniform so that the voltage across any one phase of either the master frequency source or the local frequency source is substantially the same.

In view of the fact that the source of master frequency associated with the underbraked wheel unit supplies power to the phase windings Al and BI of all of the relays 92 whereas the sources of local frequency are required to supply power only to the one set of phase windings A2 and B2 of the corresponding relay, it may be desirable to provide a two-phase alternating-current generator driven according to the speed of rotation of the underbraked wheel unit so as to obtain adequate power to properly energize the phase windings Al and BI of all of the relays on the vehicle. It is necessary, however, that th voltage characteristic of the generator simulate closely the voltage characteristic of the sources of local frequency.

If it is desired to have the vehicle travel in either a forward or a reverse direction it is necessary to provide suitable reversing switch means (not shown) preferably automatically responsive to a change in direction of rotation of the wheel axles or of the wheels themselves, to reverse the connections to one of the phase windings of each set on the relays 92, such as the connections to phase windings Al and A2.

The necessity for reversing the connections to one of the phase windings of each group upon reversal of the direction of rotation of the vehicle wheels will be apparent from the fact that the phase rotation of the polyphase voltages supplied to the respective sets of windings of the relays 32 reverses with a reversal of direction of rotation of the wheels l3, which in turn results in a reversal of the direction of application of the torques respectively exerted by the two sets of windings of the relays on the rotor 52 thereof. In order to cause the rotor 52 to move in the right direction to effect engagement of the contact 59 tion when wheel slip occurs.

Operation of equipment shown in Fig. 1

Let it be assumed that a single car having the equipment shown in Fig. l is traveling along the road under power with the brake valve handle Illa in its brake release position and that the operator desires to effect an application of the brakes. To do so, the operator first shuts oil propulsion power and then operates the brake valve handle i9a into the application zone an amount corresponding to the desired degree of. application of the brakes. The control pipe i1 is accordingly charged to a pressure corresponding to the position of the brake valve handle, for example fifty pounds per square inch. Being connected through the branch pipes I! to the control pipe, brake cylinders ii are charged with fluid at a pressure equal to that in the control pipe and thus effect application of the brakes associated with the wheels II to a corresponding degree.

As long as the wheel units continue to rotate at a speed corresponding to car speed without slipping, the magnet valves 3| remain deenergized and consequently no variation of the pressure in the brake cylinders i5 occurs except that resulting from variations of the pressure in the control pipe I! by operations of the brake valve i9.

If during an application of the brakes, however, any of the wheel units other than the underbraked wheel unit begins to slip, the reduction in the 1ocal frequency supplied to the phase windings A2 and B2 of the corresponding relay 32 with respect to the master frequency supplied to the phase windings AI and Bi results in operation of the contact arm 54 of the relay to establish the previously described circuit for energizing the magnet winding of the magnet valve 3| for the corresponding wheel truck. The magnet valve Si is accordingly operated to cutoil the supply of fluid under pressure to the brake cylinders of the truck having the slipping wheels and at the same time rapidly exhaust fluid under pressure from the brake cylinders.

In view of the fact that operation of the contact arm 54 of the relay 32 is effected whenever the local frequency supplied to the phase windings A2 and B2 reduces a small percentage below the master frequency supplied to the phase windings Al and Bi, the fluid pressure is so promptly and so rapidly reduced in the affected brake cylinders that the slipping wheels do not decelerate to a locked condition but begin to accelerate back toward a speed corresponding to the car speed before reaching the locked condition.

As long as the rotational speed of the slipping wheel or wheel unit varies by more than ii of the corresponding wheel truck remains energized. Fluid under pressure will accordingly continue to be vented from the brake cylinders of the truck having the slipping wheels until the slipping wheels are restored substantially to a speed corresponding to car speed.

This, even if a slipping wheel unit should decelerate momentarily to a locked condition, it cannot remain in a locked condition because the fluid under pressure continues to be released from the brake cylinders associated therewith until such time as it is restored substantially to vehicle speed.

When the slipping wheel unit is restored substantially to a speed corresponding to car speed, the contact arm 54 of the corresponding relay 32 is restored to its normal position interrupting the energizing circuit for the magnet winding 46 of the magnet valve 3| for the corresponding truck. The magnet valve ii is accordingly restored to its normally position closing the exhaust communication and restoring the supply communication to the brake cylinders. Fluid undenpressure is accordingly resupplied from the control pipe I! to the brake cylinders of the truck having the slipping wheel unit. Such supply of fluid under pressure to the brake cylinders tends to reduce the pressure in the control pipe I! but due to the pressure-maintaining feature of the brake valve I9, fluid under pressure is automatically supplied to the controlpipe l'l to maintain a pressure therein corresponding to the position of the brake valve handle, notwithstanding the supply of fluid under pressure from the control pipe to the brake cylinders. Thus when a slipping wheel is restored to a speed corresponding to car speed, the pressure restored in the brake cylinders again corresponds to that established in the control pipe I'l.

If upon the restoration of the pressure in the brake cylinders, the wheel unit again begins to slip, the above operation is repeated. At no time, therefore, are the wheels permitted toreach or remain in a locked condition and slide.

When a vehicle comes to a stop in response to application of the brakes, the operator of the vehicle may operate the brake valve H to reduce the pressure in the control pipe i'l so as to correspondingly reduce the pressure in the brake cylinders and the degree of application of the brakes to prevent undesired surge at the time of stopping. After the vehicle has been brought to a complete stop, the operator may increase the pressure in the control pipe I] and brake cylinders l5 to effect any desired degree of application of the brakes so as to hold the vehicle on any grade encountered in service.

In order to release the brakes prior to again starting the vehicle, the operator merely shifts the brake valve handle [9a to its brake release position. The pressure in the control pipe I1 and correspondingly in the brake cylinders I5 is reduced to atmosphere by the exhaust of fluid under pressure through the exhaust port and pipe 28 in the brake valve and the brakes are thus completely released.v

Adaptation of equipment to a train ofcars,

In the case of a'train of cars, the equipment shown in Fig. 1 may be utilized in several ways. For example, in the case of modern high speed streamlined trains of the articulated type in which a particular group of cars and a locomotive remain coupled and do not operate ordinarly except in such trains, the train wires 31, 38 and 39 may be extended throughout the train,

ings A2 and B2.

with suitable flexible couplers 4i connecting the sections on successive cars, and only one twophase master frequency supply provided as on the locomotive. In a similar manner, the bus wires 86 and 9| may be extended throughout all cars oi the train so that only one source corresponding to the battery 80 is required on one of the cars, such as the locomotive. Likewise the wire 62 may be extended throughout all cars of the train so that only one source of current corresponding to the battery 83 need be provided on one of the cars, such as the locomotive, for energizing the magnet windings of the magnet valves 3| on the several cars.

\ On the other hand, if desired, each car may operate as a separate unit with respect to the control of the relays 32 thereon. In such case, each car requires a master frequency supply corresponding to that associated with the underbraked wheel unit in Fig. 1 and no connection between the section of wires 31, 38, I9, 62, 88 and 0| on the several cars need be eiiected. In addition, each car would be provided with separate sources of direct-current corresponding to the batteries 83 and 8!.

Modification shown in Fig. 3

Referring to Fig. 3, a modified form of relay 32a may be provided in place of the relays 32 in Fig. 1. The relay 32a diflers from the relay 32 in that a wound rotor 52a is provided instead of the squirrel-cage rotor 52. The windings on the rotor We are two-phase in character and designated A2 and B2 for the reason that current is supplied thereto by the local source of two-phase current associated with the corresponding wheel unit. In view of the fact that the rotary movement of the rotor 52a is small, flexible lead wires are provided to connect the secondary windings 34s and 38s oi the local source of two-phase current to the phase wind-- If desired, however, the rotor' 520. may be provided with three conventional collector rings to which the phase windings A2 and B2 are respectively connected; and the connections to the secondary windings oi the transformers 34 and 35 may be made through brushes contacting the three collector rings in manner not shown.

The phase windings Al and BI are arranged in the stator frame Ila in the same manner as in the relay 32.

The phase windings Al and Bi of relay 32a produce a rotating magnetic field which causes a torque to be exerted on the rotor 52a. in a direction to operate the contact arm 54 in a counterclockwise direction so as to eil'ect engagement of the contact 58 thereon with the associated pair of stationary contacts 59 and 60.

The phase windings A2 and B2 on the rotor 52a are so arranged and connected as to produce a magnetic field rotating in the opposite direction and causing a torque to be exerted on the rotor 52a in the opposite direction and maintaining the contact arm 54 in engagement with the stop it as long as the respective frequencies 01 the two-phase current supplied to the phase windings in :the stator and in the rotor do not diner by more than a certain small percentage.

When a wheel unit slips and the frequency 01' the two-phase currentsupplied to the phase windings A2 and B2on the rotor 52a is reduced relative to the frequency of the two-phase current supplied to the'istator phase windings Al and Bi, the unbalanced torque exerted on the Summary Summarizing, it will be seen that we have provided a novel arrangement for detecting a differential in the speeds of two separately rotatable elements. This arrangement comprises a relay of the induction motor type in either of two forms. In one form, one set of two-phase windings is arranged in the stator portion 01' the relay and energized by a two-phase supply at a frequency proportional to the speed of one oi the rotatable elements so as to produce a magnetic field rotatable in one direction and exerting a torque on a squarrel-cage rotor in a corresponding direction. Another set of two-phase wind- 7 ings is arranged in the stator of the relay and energized at a frequency corresponding to the rotational speed of the other rotary element so as to produce a magnetic field rotating in the opposite direction and exerting an equivalent or slightly greater torque in the opposite direction on the squirrel-cage rotor.

As long as the frequency of the two-phase alternating current supplied respectively to the two sets oi' two-phase windings does not diilfer by more than a certain percentage, the squirrelcage rotor remains in a certain normal position maintaining a contact arm thereof in circuitopen position. When the frequency of the twophase supply to one of the sets of windings differs by more than'a certain amount from the frequency of the two-phase supply to the other set of windings, the unbalanced torque on the rotor rotates it a limited amount in a corresponding direction to eil'ect movement of the contact arm to a circuit-closing position.

We have utilized the above-described arrangement to compare the rotational speeds of individual wheel units on a vehicle with the rotational speed of a wheel unit which rotates at all times in correspondence with the speed 01' the vehicle as a means for detecting the slipping condition oi the wheels and eflecting a rapid reduction in the degree of application associated with the slipping wheels so as to cause them to be restored to a speed corresponding to vehicle speed zitlllirout decelerating to a locked condition and A modified form of two-phase relay oi the instator of the relay and the other set 01' phase windings is provided on the rotor of the relay.

While we have illustrated our invention in connection with a specific form of brake control equipment, it will be understood that the specific form of brake control shown and described is immaterial and that other types of brake control equipment may also be provided without departing from the spirit or our invention. It will also be clear that while our invention has been illustrated and applied particularly in connection with a brake control equipment for vehicles, that the basic principles thereoi' may be employed in other situations wherever it is desired to detect a diflerence in the rotational speeds of two separately rotatable elements. It is accordingly not our intention to limit the scope of our invention except in accordance with the terms of the eppended claims.

Having now described our invention, what we claim as new and desire to secure by Letters Patent is:

1. Apparatus for detecting a difference in the rotational speeds of two separately rotatable elements comprising, in combination, means for supplying a polyphase voltage at a frequency proportional to the rotational speed of one of said rotatable elements; means for supplying a polyphase voltage at a frequency proportional to the rotational speed of the other of said two rotatable elements; and a relay device of the induction motor type having one set of polyphase stator windings energized by current supplied from one of said polyphase voltage supply means to produce a magnetic field rotating in one direction, a second set of polyphase stator windings energized by current supplied from the other of said polyphase voltage supply means so as to produce a magnetic field rotating in the opposite direction, and a rotor subject in substantially balanced relation to the opposing torques exerted thereon by said rotating magnetic fields and maintained in a given position as long as the frequencies of the polyphase currents supplied to the two sets of windings respectively do not differ by more than a certain amount and operative out of its normal position upon the occurrence of a predetermined difference in the frequencies of the polyphase currents supplied to the two sets of windings respectively.

2. Apparatus for detecting a difference in the rotational speeds of two rotary elements comprising, in combination, means for supplying a polyphase voltage at a frequency proportional to the rotational speedof one of the rotary elements; means for supplying a polyphase voltage at a frequency proportional to the rotational speed of the other oi. said rotary elements; and a relay device of the induction motor type having a stator provided with two sets of polyphase windings, one of which sets of windings is energized by current supplied from one of said polyphase supply means and adapted to produce a magnetic field rotating in one direction and the other of which sets of windings is energized by current supplied from the other of said polyphase supply means and adapted to produce a magnetic field rotating in the opposite directions rotor on which the torque forces resulting from the two rotating magnetic fields are exerted in opposing substantially balanced relation as long as the frequencies of the polyphase currents supplied to the two sets of windings do not differ by more than a predetermined amount and adapted to be rotarily moved out of its normal position upon the occurrence of a predetermined difference in the frequencies of the polyphase voltages supplied to the two sets of windings respectively, and switch means operated in response to the rotary movement of the said rotor.

3. Apparatus for detecting a diiferencein the frequency of two polyphase voltage sources comprising, in combination, a stator element having two sets of windings, one of which sets of windings is energized by current supplied from one of said sources and is effective to produce a mag netic field rotating in one direction and the other of which sets of windings is energized by current supplied from the other of said sources and is adapted to produce a magnetic field rotating ratus comprising the combination of a first set of polyphase stator windings effective when energized by current supplied from one of said voltage sources to produce a magnetic field rotating in one direction, a second set of polyphase stator windings effective when energized by current supplied from the other of said voltage sources to produce a magnetic field rotating in the opposite direction, and a rotor of the squirrel-cage type associated with said sets of windings in a manner such that torque forces are exerted thereon due to said rotating magnetic fields, the direction of torque in each case corresponding to the direction of rotation of the magnetic field and varying in degree according to the speed of rotation of the magnetic field, said rotor remaining stationary due to the substantially balanced relation of the torque forces thereon when the respective frequencies of the two voltage sources do not differ by more than a certain amount and being moved rotarily due to the unbalanced torque forces thereon occurring when the respective frequencies of the two voltage sources differs by more than said certain amount.

5. A device for registering the relation of the frequency of one polyphase voltage source to the frequency of a second polyphase voltage source, said device comprising the combination of a first set of polyphase stator windings effective when energized by current supplied from one of the voltage sources to produce a magnetic field rotating in one direction at a speed corresponding to the frequency of the voltage source, a second set of polyphase stator windings effective when energized by current supplied from the other of said voltage sources to produce a magnetic field rotating in the opposite direction at a speed corresponding to the frequency of the said other voltage source, a rotor of the squirrel-cage type associated with said one and said other sets of I polyphase stator windings in a manner to have opposing torques exerted thereon in response to the rotation of the respective magnetic fields which torque forces vary respectively in accordance with the rotational speed of the corresponding magnetic fields, resilient means cooperating with said rotor to maintain it in a certain normal position as long as the torque forces exerted thereon are in substantially balanced relation and yieldingly permitting a rotative movement of the rotor out of said normal position in response to an unbalance between the respective torque forces exerted on the said rotor exceeding a certain amount, and switch means operative in response to a predetermined displacement of said rotor out of its said certain position.

JOHN CANE'I'IA PAUL N BOBBART, 

